FUNCTION: This gene is specifically expressed in Schwann cells of the peripheral nervous system and encodes a type I transmembrane glycoprotein that is a major structural protein of the peripheral myelin sheath. The encoded protein contains a large hydrophobic extracellular domain and a smaller basic intracellular domain, which are essential for the formation and stabilization of the multilamellar structure of the compact myelin. Mutations in the orthologous gene in human are associated with myelinating neuropathies. A recent study showed that two isoforms are produced from the same mRNA by use of alternative in-frame translation termination codons via a stop codon readthrough mechanism. Alternatively spliced transcript variants have also been found for this gene. [provided by RefSeq, Oct 2015] PHENOTYPE: Mice homozygous for a spontaneous mutation exhibit premature death, infertility, neurological behavior defects, and demyelination. Mice homozygous for a knock-out allele exhibit abnormal myelination and neurological behavior defects. [provided by MGI curators]